whenever I try to connect to a server this error message appears:

kinda need more info but maybee u downloaded the wrong vertion of a mod? check to see the latest releases of the game! or somethings out of date.... normaly why it differs from servers

I know everything's in date and installed right

hmmmm ok well post it coz u never know something mite not say as much as you can about what youve install and have you had steam working before and able to connect to severs?

check the installation files... You have to install NS3.0 Beta 1 (155MB) and then NS3.0 Beta 3 patch (25MB)... Also check for the version of the server if it matches your version (beta 3) (look at the name of the server)...

If you still get a client.dll error... probably beta3 patch is installed at a different place... search your comp for folders called nsp; if more than 1 exists thats the case...

Oh just realized the background... it is the default for NS2.0... You've installed or trying to install over NS2.0... Ns3.0 is a standalone mode... just download and install the 2 files I mentioned above... You can find them in download section of the frontpage...

Be carefull: NS3.0 Beta 1 install installes to default steam location c:\program files\steam\steamapps\email\half-life\nsp... if you installed steam to a different drive or folder than you have to move nsp folder to right place(half-life folder in your steam install)...